<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <form id="submit">
        <p><input type="text" id="user"></p>
        <input type="submit">
    </form>
    <script>
        // 当表单的submit按钮被点击的时候，表单会触发onsubmit事件
        var submit =document.getElementById("submit");
        var user = document.getElementById("user");
        submit.onsubmit = function(event){
            // alert(1);
            if(user.value=="xiaomingjun"){
                window.location.href="https://www.taobao.com";
            }
            event.preventDefault();
        }
    </script>
</body>
</html>